Patent Document 1 as listed below discloses an optical disk apparatus that includes an optical pickup, which emits laser light to an optical disk and receives reflected light from the optical disk, a servo signal generation section (error signal generation section), which generates servo signals (servo error signals) by using electric signals based on the reflected light, a servo signal control section (gain tuning section), which controls the servo signals whose offsets are adjusted so that the amplitude of servo signals will be kept constant.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-297454